Technical Abstract:
Water-soluble anionic polyacrylamide (PAM) is employed in furrow irrigation to control soil erosion and increase infiltration. We hypothesized that post-irrigation deep percolation and preferential-flow patterns for the PAM treatment would differ from that of the conventionally irrigated (CI) furrows. Portneuf silt loam plots 179 m long were planted to corn. In PAM furrows, we added PAM to advancing irrigation streams at 10 ppm. Vacuum assisted percolation samplers at 1.2 m depth and neutron probe access tubes were installed at locations 30 m down furrow to monitor soil water flux and soil wetting patterns. Daily deep percolation volumes were collected after two irrigation events in 1998, and analyzed for nitrate-N and Cl concentrations. Under C1, percolation rate started high the first day after irrigation (1st peak), declined during the 2nd and 3rd days to a value about half of the 1st-peak value. PAM percolation peaked at about twice the initial rate on day two, then declined on the 3rd day. Percolation from both treatments attained a 2nd peak between 5 and 9 days after irrigation. Sample nitrate and chloride concentrations generally showed little relationship with sampler percolation rate. PAM treatment inhibited initial rapid downward movement of applied water, possibly by reducing preferential flow.